1. Field of the Invention
The present invention relates to an optical coordinate-input system in which information on the position of a specific portion on a display surface that has been designated by a light-obstructing object such as a finger tip is inputted as coordinate data to an information processing apparatus such as a host computer.
2. Description of the Related Art
Optical coordinate-input apparatuses for obtaining coordinate data concerning a specific portion on a display surface of a display such as a CRT or an LCD, or on a surface of printing paper are known as touch panels or touch screens.
Such an optical coordinate-input apparatus includes an XY coordinate space which is formed on the front surface of a display and on which a two-dimensional scanning means is disposed. The two-dimensional scanning means comprises a plurality of pairs of light-emitting and light-receiving elements disposed on mutually opposing sides of the display surface forming an X and Y coordinate system. The light-emitting elements arranged along each of the X and Y axes are caused to sequentially emit light so as to perform two-dimensional scanning of the display surface with light beams. The coordinates of the position where light has been interrupted by a light-obstructing object, such as the tip of a finger or a pen that accessed to the display surface in order to designate the position of a specific portion of the display surface, are calculated to be used as input data.
FIG. 2 is a schematic illustration used to explain how such a known optical coordinate-input apparatus detects the coordinates at a specific position. The apparatus includes a display surface 1, a light-emitting element array (light emitting diode (LED) array) 2 extending along the X coordinate axis, a light-receiving element array (phototransistor (PTR) array) 3 extending along the X coordinate axis, a light-emitting element array (LED array) 4 extending along the Y coordinate axis, and a light-receiving element array (PTR array) 5 extending along the Y coordinate axis.
With this construction, the display surface is scanned in such a manner that light beams sequentially emitted by a plurality of light-emitting elements in the LED arrays 2 and 4 are sequentially received by a plurality of light-receiving elements in the PTR arrays 3 and 5 in accordance with the counts of a scan counter, not shown. The count values for particular PTRs to which the transmission of light beams from the mated LEDs has been interrupted are held. The count values or values calculated on the basis of the count values are sent to an external apparatus such as a host computer.
If the transmission of light beams has been interrupted at, for instance, a portion denoted by the symbol A in FIG. 2, data on the X and Y coordinates, in this case, 6 and 7, respectively, is held and sent out.
If the interruption of light beams occurs over a relatively large area dented by the symbol B in FIG. 2, the conventional practice is to hold only the coordinates at the center of the area B, which are then sent out.
An example of an apparatus of the above-described type is disclosed in Japanese Patent Publication No. 4929/1982.
In the prior art such as that described above, elements in the LED arrays are caused to sequentially perform scanning. When light beams from certain LEDs have been interrupted by the tip of a finger or a pen that accessed to the display surface in order to designate a specific position on the display surface, the coordinates detected by the mated PTRs are sent as numerical data such as hexadecimal (HEX) codes to an external processing apparatus such as a host computer. Before the host computer is able to use the sent data, the data must be subjected to numerical calculations.
The prior art also has the following drawback. When light beams have been interrupted over a relatively large area, such as that denoted at B in FIG. 2, only the center coordinates are sent out, as described before. The information processing side, e.g., the host computer, is not informed of whether the portion of the display surface where the interruption of light beams has occurred is a two-dimensional area or a point. In order to allow informing, it is necessary, if the light-interrupted portion is an area, to send data in the form of a large number of digits corresponding to those LED-PTR pairs which cover the portion where the light interruption has occurred.